Fix the inveracious logging.Logger to customize.

[louyuting]

Describe what this PR does / why we need it

In logging module, current implementation cannot customize Logger implementation by user.
Current exported function, logging.ResetDefaultLogger(), is not working as expected.

Does this pull request fix one issue?

Describe how you did it

Describe how to verify it

Special notes for reviews

[codecov-commenter]

Codecov Report

Merging #201 into master will decrease coverage by 0.26%.
The diff coverage is 14.43%.

@@            Coverage Diff             @@
##           master     #201      +/-   ##
==========================================
- Coverage   44.25%   43.99%   -0.27%     
==========================================
  Files          80       80              
  Lines        4424     4453      +29     
==========================================
+ Hits         1958     1959       +1     
- Misses       2236     2264      +28     
  Partials      230      230              

Impacted Files	Coverage Δ
api/tracer.go	37.50% <0.00%> (ø)
core/circuitbreaker/circuit_breaker.go	23.56% <0.00%> (ø)
core/circuitbreaker/rule.go	84.10% <0.00%> (ø)
core/flow/slot.go	0.00% <0.00%> (ø)
core/hotspot/cache/lru.go	53.77% <0.00%> (ø)
core/hotspot/concurrency_stat_slot.go	0.00% <0.00%> (ø)
core/hotspot/slot.go	33.33% <0.00%> (ø)
core/hotspot/traffic_shaping.go	63.15% <0.00%> (ø)
core/log/metric/aggregator.go	29.16% <0.00%> (ø)
core/log/metric/reader.go	0.00% <0.00%> (ø)
... and 21 more

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[eddycjy]

Thanks for the fix, I think it is basically available.

[sczyh30]

LGTM

[sczyh30]

Nice work. Thanks!